Forming precise reinforced recesses in thermoplastic foams

ABSTRACT

The invention relates to a novel method for making improved packaging components of thermoplastic foam. Recesses of predetermined size, shape and depth are pressed into sheets of the foam material by the combined effect of a die or hob structure maintained at a temperature which will not melt, but will substantially soften the material, such structure being forced into the material by a pressure which would be inadequate to effect penetration if the material were not progressively softened as the die advances. Each work piece is pre-coated on the face to be recessed with an appropriate release agent. The lateral walls of the recess are protected against heat shrinkage by limitation of temperature and by speed of penetration together with limitation of lateral die area. The material displaced by recess formation is all usefully employed through fusion and condensation to reinforce the wills of the components in the very areas where they are thinned and where the merchandise is to be nested in them.

Unite States Edwards et a1.

atent 1 June 13, 1972 [72] Inventors: Clarence K. Edwards, 865 MorrisonStreet; Lawrence D. Edwards, 2816 Rosemont Avenue, both of Medford,Oreg. 97501 [22] Filed: Nov. 4, 1969 [21] Appl.N0.: 873,953

[52] US. Cl ..264/l30, 264/321, 264/322 3,530,213 9/1970 Belle ..264/32lX Primary Examiner-Robert F. White Assistant ExaminerRichard R. KuciaAttorney-Clarence M. Crews ABSTRACT The invention relates to a novelmethod for making improved packaging components of thermoplastic foam.Recesses of predetermined size, shape and depth are pressed into sheetsof the foam material by the combined effect of a die or hob structuremaintained at a temperature which will not melt, but will substantiallysoften the material, such structure being forced into the material by apressure which would be inadequate to effect penetration if the materialwere not progressively softened as the die advances. Each work piece ispre-coated on the face to be recessed with an appropriate release agent.The lateral walls of the recess are protected against heat shrinkage bylimitation of temperature and by speed of penetration together withlimitation of lateral die area. The material displaced by recessformation is all usefully employed through fusion and condensation toreinforce the wills of the components in the very areas where they arethinned and where the merchandise is to be nested in them.

4 Claims, 7 Drawing Figures FORMING PRECISE REINFORCED RECESSES INTHERMOPLASTIC FOAMS The packaging components of foam material and themachine for making packaging components disclosed in this specificationare not claimed herein, but they are claimed respectively in divisionalapplications Ser. No. 194,229 and Ser. No. 194,146, both filed Nov. 1,1971.

This invention relates to packaging components, more particularly topackaging components made from materials of the aerated thermoplastictype, and their manufacture. Such materials are generally referred to asfoams and consist, as a rule, of numberless small beads, cells orbubbles of thermoplastic material, such as polystyrene, united into ahomogeneous mass. A package in which such material is used generallyincludes two complementary, firm but cushioning sections of stableconfiguration, having flat confronting surfaces in marginal areas andoptionally in some interior areas, but formed with one or more opposedcavities or recesses which fit and contain portions of the object orobjects being shipped. The composite foam structure may completelyenclose the merchandise, or the two components may be spaced far apartif the contained merchandise is adapted to space them in definitelyfixed relation to one another when placed in a carton of appropriatesize and shape.

The primary purpose of these components is to cushion the merchandisewhile providing a definite compartment for each item, in which the itemis at least partially confined, and providing exteriorly a compositeorganization of fixed dimensions, adapted to fit snugly into anenclosing carton.

The foams are generally light, weighing in the neighborhood of one tothree pounds per cubic foot, but sometimes considerably more. They holdtheir shapes, and, when made in accordance with the present invention,stand up under rough usage.

The formation of the foam materials into packaging components presentsunique problems because of the nature of the material. The material whensubjected to heat does not have a definite melting point. For eachmaterial there is a temperature at which it starts to soften, then, asthe temperature rises, to lose shape and to become sticky and somewhatfluid. If a source of heat sufficiently intense to melt nearby materialis brought near enough to melt the skins of the outer beads and collapsethe beads, the cellular material appears to recoil and shrink as onebead layer after another is reduced to a fluid state. When such acondition is allowed to last for any substantial time, sharp definitionand accurate shaping are not possible in the affected area.

Up to the present time there have been three methods of making packagingcomponents of foam material. The first two are slow, costly as regardslabor, and produce components which are weak in the thinned areas. As aconsequence the resulting components have been expensive to make and,for some services at least, deficient in performance. Components made bysuch methods have not, therefore, been economically available in someinstances, and/or have not had the required durability and strength.

The first of these methods is performed in an expensive mold of the kindused for die casting, but because of the nature of the material employedthe process does not resemble die casting at all. Instead of injectingmolten material into a chilled cavity to solidify, bubbles are blowncold into the cold cavity. Steam is then injected into the mold to heatthe mold and to soften the beads and make them tacky so they will adhereto one another. The steam also expands the bubbles, making the productlighter than it would otherwise be. The mold and its contents are thencooled to about 80 F. and the resulting component is removed. This is avery slow and time consuming cycle, involving high labor cost andexpensive equipment, long heating, cooking and cooling periods, and anextravagant utilization of steam under pressure. The product is ofuniform composition and density throughout and therefore of unevenstrength, being weakest where the recesses or cavities cause the wallsto be thinnest.

The second procedure does not involve the use of heat. A flat sheet offoam material of uniform thickness is provided as the work piece and thematerial is routed out in the areas where the cavities are to beprovided.

Starting material for this purpose can be provided at moderate cost,either by a continuous extrusion process or by the molding of large,thick blocks which are then sliced into slabs or sheets of the desiredthickness. A typical block may measure 4 feet by 8 feet by l and A feet.

The routing out of the material is a slow operation, however, involvingmuch labor expense. Again, the material is of uniform structure anddensity throughout the finished component, so that the component is weakin the thin areas, the very areas in which the merchandise is to benested and in which reinforcement is most needed.

The third method also starts with a flat sheet of foam material ofuniform thickness. it is a cold compression method which has limiteduses at best. It requires the application of such a high pressure thateven the unrecessed face may be seriously impaired, particularly in thethinned areas. It is inapplicable to most of the foam materials becausethe materials have enough resiliency immediately to recover more orless, and to tend gradually to recover further, the result being thatcavities of predetermined dimensions cannot be dependably formed andmaintained. Again the resulting component is not reinforced in thethinned areas.

We have contrived a novel apparatus and method which, because of reducedlabor cost, reduced cost of dies and other equipment, and increaseddependability, reduces the cost of production of thermoplastic foam typepackaging components by at least 50 to 67 percent, while improving theproduct significantly.

The starting material is desirably a foam sheet or slab of moderate, anddesirably uniform thickness. In the areas to be recessed the material ispressed between a heated die and a sheet holder under a limited constantpressure which would be insufficient to cause the unheated die topenetrate the material over any substantial area. The die is, however,maintained at a temperature sufficiently elevated to soften the surfacematerial and cause it to become tacky but not freely fluid. Penetrationprogresses only as the material in the die contacted area becomes softenough to yield under the limited pressure which is applied.

The material, whose softening or fusion permits the die to penetrate, isflowed under pressure to form a skin reinforcement in the nesting orthinned areas. All the original foam material is thus preserved and putto use in strengthening the thinned areas, so that a superior productresults.

When the die has penetrated the foam material to the desired depth, atripper reverses the relative movement of the die and the sheet holder,leaving the finished component in the holder. There is no alternateheating and cooling of the die, and while the rate of die penetrationmay vary a little with slight variations of temperature which may occur,the complete loading, operating and unloading cycle runs to about 25 to30 seconds, not more than H l 2 the time required for the completeforming cycle by the method first outlined above. As many components maybe made simultaneously as the chosen size of the press will permit. Theproduct is uniformly sharply formed to the desired outlines, thepercentage of rejects being very small.

it is essential to the invention that a molding press be providedeffective to form desired, sharply defined, cavities or recesses insheeted foam material through a combination of limited predeterminedpressure together with limited predetermined heat softening and fusion.

It is also essential that the molding press of the kind referred toshall comprise a heated platen to which dies or hobs of various designsand contours may be selectively applied. Dies of this kind can befurnished at a small fraction of the cost of dies of the kind requiredin carrying out the method first outlined above. There are no coolingjackets, no passages for coolant, no passages for steam injection, nocomplicated patterns to contrive. In other words, the apparatus isreduced to that required for simple hot pressure molding of materials ofthe kind referred to.

It is important that in the molding press the work holder and the heateddie are relatively advanced toward one another at a rate controlled bythe combined effect upon the work piece of sufficient heat to produceprogressive, gradual fusion as the die advances and under a limitedpressure, until a predetermined penetration has been effected, togetherwith means for thereupon reversing the relative movement of thecomponent holder and the die.

It is a still further object to provide a method or procedure formolding cavities in foam material in which the heated die at theconclusion of the stamping stroke is withdrawn cleanly from the formedcomponent without imposing surface damage or damaging strain on thecomponent, through sticking of the component to the die. To this end itis an important point that each blank of sheet material is pre-coated onthe die-engaged face with a liquid coating of a suitable release agent.Each blank leaves a slight residual coating of the solids contained inthe release agent on the blank engaging die surfaces, and this affectsbeneficially the release of the next following blank. For sharpness ofdefinition it is important for the release to be effectedinstantaneously at the point of reversal. The release agent desirablyincludes water as a vehicle, and this serves effectively to protect theareas not engaged by the die, but closely adjacent to the engaged areas,against possible heat deformation. These areas come out of the machinewet, and, therefore, without having been heated above the boiling pointof water.

It is a further object to produce recessed packaging components fromsheets of foam material, at less cost, and at the same time offunctionally superior quality a compared with foam packaging componentsheretofore available.

Other objects and advantages will hereinafter appear.

In the drawing forming part of this specification:

FIG. 1 is a view in side elevation of a molding machine of simpleconstruction, the machine being designed to convert identical sheets ofthermoplastic foam material into complementary packaging componentsthrough the molding of complementary cavities or recesses therein;

FIG. 2 is a view in front elevation of the machine of FIG. 1;

FIG. 3 is a plan view of a packaging component formed with circularrecesses for use in shipping canned goods;

FIG. 4 is a view in elevation showing two components of the kindillustrated in FIG. 3, the components being associated with oppositeends of a suitable number of cans in an assembly which will snugly fitwithin a rectangular carton of appropriate dimensions;

FIG. 5 is a plan view of one of two complementary formed componentswhich, when brought together form suitable closed compartments forcompletely enclosing a stapler and certain accessories and/or supplies;

FIG. 6 is a diagrammatic view showing the hydraulic and electricalsystems of the illustrative machine; and

FIG. 7 is an edge view showing the electrically heated platen andcomposite molding die means affixed thereto, as used in the machine ofFIGS. 1, 2 and 6.

THE MACHINE The machine 10 is fixedly mounted on a rigid framework ortable 12. The table 12 comprises vertical legs 14, lower, intermediateand upper longitudinal bars 16, 18 and 20, and lower, and intermediatetransverse bars 22 and 24, and an upper transverse bar (not shown).

Beneath the table top 28, the table framework provides support for ahydraulic fluid reservoir or sump 30, a variable volume hydraulic pump32 and a pump motor 34.

The table top 28 supports four upstanding corner posts 36 upon which awork piece holder and carrier 38 is guided for vertical movement. Thecarrier 38 normally rests upon collars 40 affixed to the posts 36, andis adapted to be thrust upward by a hydraulic operating ram 42, to whichit is attached. The ram 42 is a rigid structure which includes a pistonrod 44 that extends downward into a stationary hydraulic cylinder 46.

The work piece carrier 38 has mounted on its upper surface front andrear, overhanging guide members 48, beneath which the margins of twowork pieces can be simultaneously manually fitted from opposite sides ofthe machine by the operator. A partition member 50 divides the spacebetween the front and rear guide members 48 and serves as a stop forlimiting the insertion of the work pieces to predetermined positions, sothat each will be carried upward in precisely the desired relation toone of two molding dies 52. The molding dies are designed to producecomplementary recesses and may, in an appropriate case, be mirror imagesof one another.

The upper ends of the rods 36 support in fixed position a molding diesupporting plate 54, to which, through suitable spacers 56, anelectrically heated platen 58 is fixedly attached. The platen 58 is amassive plate having electrical heating elements 60 mounted within it.Each die 52 comprises a mounting plate 62 which is secured to the platen58 in extensive, heat conducting contact therewith by screws 64. Eachdie 52 also includes one or more hobbing projections or die components66 of suitable pattern, detachably connected to its mounting plate 62 byscrews 68. The hobbing projections 66 in the illustrative machine arezinc castings, but other metals and alloys such as copper, brass,bronze, stainless steel, aluminum and probably others, so long as theyare non-corroding, highly heat conductive, and solid at the operatingtemperature, would serve.

It is an important point that each hobbing projection is formed on itswork engaging surface with a continuous, thin, overhanging lip orperipheral flange 70 of substantial width. The importance of thisfeature will be made clear presently.

A thermometer 72 is applied to an edge face of the platen and the platenheating means can be set to maintain the platen at substantially apredetermined temperature, or within a narrow predetermined temperaturerange.

The hydraulic and electrical systems of the illustrative machine arediagrammatically shown in FIG. 6.

A three wire A. C. electrical system 74, comprising wires 76, 78 and 80,supplied from a suitable source, is normally open-circuited, but it maybe activated through operation of a three pole, single throw masterswitch 82 to closed position. This makes current available both to thecircuit of the pump motor 34 and for other purposes as will be pointedout. Since it is not desired to start the pump until after the platenhas been warmed to operating temperature, an on-off switch 88 isprovided for controlling only the operation of the pump.

The closing of switch 82 energizes the primary winding 90 of atransformer 92, thereby inducing in the secondary winding 94, having thesame number of turns as the primary winding, alternating current of thesame frequency and voltage as that flowing in the primary. The inducedcurrent may be assumed to have a potential of 240 volts. From thewinding 94 a circuit can be traced through a conductor 96, one elementof a two pole switch 98, conductor and a settable, thermostatic control102, to the platen heating resistors 60, which are connected in parallelrelation with one another and with a pilot light 104. The return isthrough a conductor 106, the second element of switch 98 and conductor108 to the second terminal of secondary winding 94.

The remaining circuitry has to do with the control of the hydraulicsystem. As soon as the platen has reached the operating temperature(desirably 350 F. when polystyrene foam, which begins to soften at 290F., is used) the switch 88 is closed and the pump 32 is caused to runcontinuously. The pump 32 draws hydraulic fluid from the reservoir 30and delivers it to a conduit 112.

An emergency relief valve 114 interposed between the pressure conduit112 and a reservoir return conduit 116 is set to become effective at ahigher pressure than that for which a regulator 118 is set. Theregulator 118 can be set to maintain any desired constant pressure inconduits 112 and 120. Surplus hydraulic fluid is by-passed to thereservoir return conduit l 16, through a conduit 122.

The conduits 116 and 120 are, through a solenoid operated slide valve128, reversibly connected to conduits 124 and 126, which latter conduitsare in constant communication, respectively, with the upper and lowerends of cylinder 46. In FIG. 6 the valve is in its normal, idle,right-hand position, a position in which it is normally maintained by acompression coil spring 130. In this position the establishedconnections are such that the hydraulic fluid would be delivered underpressure to the upper end of cylinder 46 through conduit 124 and woulddrive downward a piston head 132 which forms part of the ram 42, but forthe fact that the piston 132 is at the lower limit of its movement, sothat no more hydraulic fluid can enter the upper end of the cylinder.All the hydraulic fluid delivered by the pump, therefore, is bypassed bythe regulator 1 18 through conduit 122 to reservoir return conduit 116.The machine, in the condition shown, awaits the introduction of a freshpair of work pieces into the carrier 38 and the initiation of anelectrically controlled cycle of operations by the operator.

The electrical control system includes conductors 134 and 136, theformer connected through conductor 108 to the lower terminal ofsecondary winding 94, and the latter to a center tap 138 of the samewinding. The control circuit is, therefore, furnished with one-half thevoltage of the heater and pump motor circuits. The control circuit isprepared for operation, but is not put into operation, by the manualclosing of a switch 140 which remains closed until it is manuallyopened. A pilot light 142, interposed in a line 144 which connects 134to 136, indicates to the operator that the switch 140 stands in itsclosed position.

The control circuit can be traced from 134 through a normally closedemergency switch 146, thence through a conductor 148, a normally closedswitch 150, and a conductor 152 to a terminal 154 at or just after whichthe circuit comes to a dead end with the parts in the condition in whichthey are shown in FIG. 6.

From 154 there are two potential return paths to center tap 138 througha conductor 156. One of these paths is through a normally open, relaycontrolled switch 158, a solenoid winding 160 and a conductor 162, butsince the switch 158 is normally open, this path is not directly orimmediately available. The other potential path through 156 is through abranch conductor 164, which includes a normally open relay controlledswitch 166, a conductor 168, the relay 170 which controls the closingand keeping closed of switches 158 and 166, and the conductor 162. Sincethe switch 166 is normally open, this path is not directly orimmediately available either.

The only path directly available for completing a circuit from terminal154 to center tap 138 is through a conductor 172, which includes twonormally open manual switches 174 and 176, in series with one another.When these two switches are simultaneously manually closed, a circuit iscompleted through conductor 172, a conductor 178, relay 170 andconductor 162.

The provision of the two switches 174 and 176 in series with one anotheris a familiar safety expedient. It prevents starting of the press by theaccidental closing of one of them, and it keeps both hands of theoperator occupied in locations where they are out of harm 5 way as thepress is started.

As has been noted, the closing of switches 174 and 176 causes current toflow through relay 170. This closes switches 158 and 166, causingcurrent to flow through both of these switches. The current which flowsthrough switch 166 flows also through relay 170, thus keeping the relayenergized and both switches 158 and 166 closed after the switches 174and 176 have been permitted to open. The flow of current throughsolenoid winding 160 is, therefore, also maintained.

Energization of the solenoid winding 160 causes the valve 128 to bethrust toward the left against the resistance of a compression coilspring 130. This reverses the connections of conduits 116 and 120 withconduits 124 and 126, causing hydraulic fluid to be delivered underpressure through conduit 126 to the lower end of cylinder 46 and thehydraulic fluid in the upper end of the cylinder to be dischargedthrough conduit 124.

The piston or ram, therefore, drives the work carrier 38 upward towardthe die at a good speed, but not fast enough to deal a damaging blow tothe foam material. In fact, if the pressure has been properly chosen andthe work carrier were driven up against a cold die having all hob facesdisposed in a common plane, the work pieces would not be perceptiblydented. If there is an area in which a small hob projects upwardsubstantially farther than any other, it may penetrate freely until theresistance to penetration is reinforced by the contact with other hobs.The indentation in the small area is stabilized by the softening andcondensing of material in that area at greater depths.

With polystyrene foam having a density of 1.5 pounds per cubic foot asthe material worked upon, the platen temperature may desirably be set at350 F. and the pressure at about 8.8 pounds per square inch for themaximum hob area (the hob area at maximum penetration), but both thetemperature and the pressure may be raised considerably within the scopeof the invention. The pressure here referred to would be the pressureindicated by a gauge 184, multiplied by the cross-sectional area of thepiston and divided by the maximum total hob area of the two diescombined. The gauge 184 is connected through a manually operable valve186 to the conduit 112.

Upon contact of the work pieces with the dies, the advance of the workcarrier is slowed down progressively, being permitted to continue onlyas the softening of the material makes the advance possible.

When the desired limit of penetration has been reached, a verticallyadjustable rod 182, mounted on the work carrier, and movable in unisonwith the carrier, engages and opens the switch 150. This immediatelydeenergizes the relay 170, causing switches 158 and 166 to open. This,in turn, deenergizes the solenoid winding 160, permitting the valve 128to be returned to the position of FIG. 6 by the spring 130.

This second reversal of the valve 128 causes the ram or piston, togetherwith the work carrier, to be driven downward hydraulically to thestarting positions, where they will remain until a new cycle isinitiated by simultaneous manual closing of the switches 174 and 176.

A heat exchanger 188 is interposed in the return conduit 116 for coolingthe hydraulic fluid on its way back to the reservoir. This not onlykeeps the fluid cool, but maintains it as a desired, substantiallyuniform viscosity.

If all has gone well the operator can, upon the return of the workcarrier to the normal, lower position, extract from the carrier twoperfect, sharply defined, packaging components. That all will go wellcan be quite definitely assured if the temperature and pressure areproperly adjusted to the material employed, and the particular patternsought to be impressed, and if certain other precautionary measures aregiven due attention. The percentage of rejects is very small when all ofthese factors are properly attended to.

Two component patterns are disclosed in FIGS. 3 and 5, and a packagegroup utilizing two of the FIG. 3 components is shown in FIG. 4.

The component 190 of FIG. 3 consists of a rectangular sheet, about 1inch thick and having six circular recesses 192 of equal depth, about 4inch, formed in it, the recesses being arranged in rows and columns, twoby three. Six cans 194 of the same diameter as the recesses are placedin the recesses of the lower component of FIG. 4 and the upper componentis then fitted onto the upper ends of the cans. This assembly can be puttogether inside a carton of suitable size, and the carton then closed.Alternatively, the assembly may be transferred into a carton after it isotherwise complete. This type of package has been found to be veryuseful for shipping canned goods without damage.

The component 196 of FIG. is designed to be used in conjunction with alike, complementary component for shipping a stapler together withcertain accessories and/or supplies. Different portions of thismerchandise require recesses of different depths and they are providedby providing hobs of different thicknesses, which penetrate to differentdepths, or hobs of varying thickness. These components fit together faceto face with the stapler and other contents completely enclosed.

THE METHOD The chief difficulties to be guarded against are:

1. The employment of inadequate or excessive heat, and the employment ofinadequate or excessive pressure.

2. Heat damage to the unimpressed surfaces of the work pieces whichborder the recesses, i.e., shrinkage.

3. Shrinkage of the lateral faces of the formed recesses throughexposure to excessive heat.

4. Failure to secure prompt, easy and complete release of the workpieces by the dies, and the prompt withdrawal of the work pieces at theconclusion of the forming operation.

The temperature employed depends primarily on the material used, andonly to a slight degree upon the density of the material. It should bedefinitely above the temperature at which the material begins to softenbut substantially below the temperature at which the material becomesfreely fluid. A suitable platen temperature for use with the mostcommonly used foam, polystyrene, is 350 F. This temperature is notnecessarily optimum under all conditions, but it is within a practicaland operative range. The less the pressure employed for a givenmaterial, the higher the temperature will have to be, and the greaterwill be the likelihood of heat damage.

For a given material the pressure will vary chiefly with density. As ageneral guide, a complete cycle of the machine, including unloading andloading time, should be under 30 seconds, and preferably within about 25seconds. With the temperature determined and maintained, the pressuremay be adjusted to obtain the optimum timing consistent with goodresults.

The thin but rather wide marginal overhangs 70 provided on the faces ofthe hobs protect effectively against heat damage to the lateral faces ofthe recesses, if the temperature employed is not excessive, and thepressure employed is sufficient to keep the carrier moving and assurethe prompt completion of the molding cycle.

It has been found impossible to secure consistent release of the formedcomponents by the dies at the conclusion of the forming operationwithout resort to the employment of a release agent. Ready release couldbe assured by generously spraying the faces of the dies after each cyclewith a silicone release agent, but that would be an expensive procedure,both from the standpoint of labor and material.

We have found the following procedure to be most satisfac tory anddependable:

At the very start of operations the dies are sprayed with a siliconerelease agent. The work pieces of each pair, including the very firstpair, and dipped in a release agent mixture described below. Thesedipped faces may be rubbed together for some little time, say about tenseconds, and they are then put into the machine, and the forming cycleof the machine, as described above, is executed. While the machine cycleis in progress the next pair of work pieces is dipped and rubbed.Alternatively, the release agent may be sprayed onto the faces of thework pieces. Each pair of pieces apparently leaves a residual deposit orcoating of stearate on the dies, which is beneficial in assuring thecomplete and clean separation of the following pair of work pieces. Ifthe application of the release agent is dispensed with, three or fourmore pairs will release, but with progressively deteriorating results,and then sticking will occur.

The release agent which we have found most advantageous is made up asfollows, the parts" referred to being parts by weight.

In 1,000 parts of water, 8.6 parts of Tide" detergent were dissolved,and 88 parts of zinc stearate were then stirred in. Varied percentageswould be operative, but this one has been developed as a result of anextended and persistent exploration and is considered most practicalfrom the standpoint of cost and performance. The high water content ofthe release agent is considered advantageous, both because it limits theconsumption of the other ingredients to economical operative levels, andbecause it effectively protects the work piece margins which border therecesses, against heat damage which might otherwise result fromproximity of these surfaces to the backing plate. The release agentmixture should be stirred from time to time.

THE PRODUCT The machine and method described produce an integralpackaging component at one-third to one-half the cost of the most nearlysimilar packaging component of the prior art. Such prior art packagingcomponents do not, however, closely approach in quality the product ofour machine and method. In our product all of the foam materialdisplaced by the recess forming operation is changed to a semi-fluidstate and is fused and condensed into the wall portions which arethinned by the recess formation, serving thereby materially to reinforcethe thinned portions of the walls, the portions in which the merchandiseis nested, and which are most in need of reinforcement. No packagingcomponent of the prior art has this characteristic. The possession ofthis characteristic is dependent upon the machine and the method bywhich the packaging component is produced.

These components, because of their reduced cost and increased strength,open up extensive new practical fields of use for packaging componentsof the thermoplastic foam type.

We have described what we believe to be the best embodiments of ourinvention.

We claim:

1. The method of simultaneously die molding a plurality of recesses intoan integral packaging component of the thermoplastic foam type from asheeted work piece of thermoplastic foam which comprises forcing a diewhich is equipped with a plurality of heated, forming hobs, each havinga thin peripheral flange at its leading end, rectilinearly into the workpiece in direct contact therewith, under a limited pressure which wouldbe insufficient to effect significant penetration of the material by thedie in an unheated state, while maintaining the die temperature in theheat-softening temperature range of the thermoplastic foam material withwhich it is engaged, so that the rate of penetration is made to dependupon the rate of fusion of the foam material, with the consequence thatat the conclusion of the recessing operation substantially all of thematerial displaced by the recessing will have been combined throughfusion and condensation into the portion of the component which has beenthinned by the recessing, to reinforce and strengthen such thinnedportion, and that the side walls of the resulting recesses will besharply defined and free from heat-shrinkage distortion.

2. The method of die molding an integral, recessed packaging componentof the thermoplastic foam type as set forth in claim 1 which furtherincludes the preliminary coating of the face of the foam work piecewhich is to be directly engaged and fused by the die with a suitablerelease agent, whereby the die and the recessed component are caused toleave contact with one another readily and without imposing damagingstrain upon the recessed component.

3. The method of forming a recessed packaging component of thethermoplastic foam type as set forth in claim 2 in which the releaseagent employed is carried in water as a vehicle, the water serving alsoin the areas not actually engaged by the die to limit heating of thework piece surface in such areas, thereby to prevent heat damage to thesurface in such areas.

2. The method of die molding an integral, recessed packaging componentof the thermoplastic foam type as set forth in claim 1 which furtherincludes the preliminary coating of the face of the foam work piecewhich is to be directly engaged and fused by the die with a suitablerelease agent, whereby the die and the recessed component are caused toleave contact with one another readily and without imposing damagingstrain upon the recessed component.
 3. The method of forming a recessedpackaging component of the thermoplastic foam type as set forth in claim2 in which the release agent employed is carried in water as a vehicle,the water serving also in the areas not actually engaged by the die tolimit heating of the work piece surface in such areas, thereby toprevent heat damage to the surface in such areas.
 4. The method forminga recessed packaging component of the thermoplastic foam type as setforth in claim 2 in which the release agent applied consists essentiallyof water as a vehicle, a detergent and zinc stearate in the proportionsby weight of substantially 1,000 parts water to 8.5 parts detergent to88 parts zinc stearate.